1. Field of the Invention
The present invention relates to an image stabilization control apparatus that compensate image blur (image degradation) caused by shakes such as hand shakes, and relates to control methods for such an image stabilization control apparatus, an optical apparatus, and an imaging apparatus.
2. Description of the Related Art
At present, cameras provided with image stabilization control apparatuses that prevent image blur caused by hand shakes and are configured with, for example, a shake compensation unit, a driving unit, and a shake detection unit are in commercial production, and as a result, user-caused shooting mistakes are decreasing.
Furthermore, image stabilization control apparatuses that detect rotational shakes using an angular velocity sensor and suppress image blur on the surface of an image sensor by moving part of a lens, the image sensor, or the like are employed in various types of optical apparatuses as a useful image blur compensation technique.
However, when shooting at close ranges, shooting at a high magnification ratio, and so on, image degradation caused by what are known as “translational shakes”, which act in the translational or vertical direction relative to the optical axis of the camera and cannot be detected solely by an angular velocity sensor, cannot be ignored. It is necessary to actively detect and compensate translational shakes in, for example, the case where an image is shot from approximately 20 cm from the subject, as in macro shooting, the case where the focal length of the imaging optical system is extremely long (for example, 400 mm) when the camera is approximately 1 m away from the subject, and so on.
Japanese Patent Laid-Open No. 7-225405 discloses a technique where an acceleration sensor that detects acceleration is provided, translational shakes are found from a second-order integral of the acceleration obtained by the acceleration sensor, and a shake compensation unit is driven based on the translational shake and the output of a separate angular velocity sensor.
However, the output of the acceleration sensor used to detect translational shakes is susceptible to environmental changes such as noise from disturbances, changes in temperature, and so on, and because such unstable factors are exacerbated by taking the second-order integral, there is a problem in that highly-precise translational shake compensation is difficult to achieve.
Meanwhile, Japanese Patent Laid-Open No. 2010-25962 discloses handling translational shakes as rotational shakes when the center of rotation is located in a position that is distant from the camera. With this method, an angular velocity sensor and an acceleration sensor are provided, and shake compensation is carried out by finding a compensation value and an angle using the radius of rotation of the rotational shake based on the output from the sensors; through this, a center of rotation that is limited to a frequency band unsusceptible to disturbances is found. Doing so makes it possible to reduce unstable factors in the acceleration sensor as described above.
With methods that carry out translational shake compensation using the radius of rotation of rotational shakes, it is necessary to find the radius of rotation precisely, and thus in the case where the radius of rotation is calculated using an acceleration sensor and an angular velocity sensor, the detection precision of those sensors is extremely important. However, in the case where the influence of sensor noise is high, it is difficult to find the precise radius of rotation, which in turn makes it difficult to achieve the desired translational shake compensation effects. In the case where the ratio of sensor noise to the output of the acceleration sensor is particularly high, there is the risk that the radius of rotation will be erroneously estimated, the compensation amount of translational shake will increase, and the stabilization performance will worsen due to overcorrection.
Generally speaking, the amount of sensor noise is constant regardless of the amount of acceleration, and thus in the case where translational shakes are great, or in other words, in the case where the acceleration sensor outputs a high value, the sensor noise has little effect on the estimation of the radius of rotation, and a precise compensation amount of translational shake can be found. However, in the case where the translational shakes are extremely small, or in other words, in the case where the acceleration sensor outputs a low value, the sensor noise has a significant effect on the estimation of the radius of rotation, and it is thus difficult to find a precise compensation amount of translational shake. In other words, differences arise in the detection precision of translational shakes due to differences in instability amounts caused by different shooting positions and so on, or to put it differently, differences in the stabilizing effects arise.
Meanwhile, there are situations where the user carries out shooting operations while framing the subject he or she wishes to shoot by tracking the subject, situations where the user carries out shooting operations while adjusting shift in the angle of view arising due to hand shakes, and so on. In cases such as these, translational shakes caused by the user intentionally moving the camera occur in addition to the translational shakes caused by unintentional hand shakes on the part of the user. If translational shake compensation using the radius of rotation of the rotational shakes is carried out at this time, the radius of rotation takes on an extremely high value during panning or tilting operations, which results in the possibility of the radius of rotation being erroneously estimated during shooting that immediately follows the panning or tilting operations. Specifically, there have been situations in which excessive compensation amount of translational shake employed during shooting immediately following panning or tilting operations have negatively affected the stabilization effects of the shake compensation.